The Local Interconnect Network (LIN) is a serial network protocol designed for communication between different electronic modules and devices and mainly employed in automobiles. The need for a cheap serial network arose as the technologies and the facilities implemented in an automobile grew, while the Controller Area Network (CAN) bus was too expensive to be implemented in every electronic module or device in an automobile. European car manufacturers started using different serial communication topologies, which led to compatibility problems. In the late 1990s, the LIN Consortium was founded by five automakers, and the first fully implemented version of the new LIN specification (LIN version 1.3) was published in November 2002. In September 2003, LIN version 2.0 was introduced to expand capabilities and make provisions for additional diagnostics features.
LIN is a serial network (often referred to as LIN bus) including one master device (bus master) and typically up to sixteen slave devices (bus slaves). All messages are initiated by the master device with at most one slave device responding to a given message identifier. The master device may also act as a slave device by replying to its own messages. Because all communications are initiated by the master device it is not necessary to implement a collision detection. The master device may be a microcontroller, whereas the slaves may be implemented as an application-specific integrated circuit (ASIC).
Current applications combine the cost efficiency of LIN and simple sensors to create devices or modules interconnected to form small networks. These networks may be connected to a back-bone-network, i.e., CAN in automobiles. The general terms electronic devices and electronic modules are used as synonyms herein and are often referred as electronic control units (ECUs), particularly in automotive applications. The ECUs are also referred to as “nodes” as they form the nodes of a network in accordance with the LIN specification.
The LIN specification was designed to allow very cheap hardware-nodes which are used within a network. LIN is a low-cost, single-wire network based on ISO 9141. The LIN master nodes are often implemented using microcontrollers with either UART capability or dedicated LIN interfaces. The microcontroller generates all the LIN data (in accordance with the LIN protocol) using appropriate software and is connected to the LIN network via a LIN transceiver. Operating as a LIN master node may only be part of the possible functionality of the device. However, the LIN hardware may include the mentioned transceiver and works as a pure LIN node without added functionality.
As LIN slave nodes should be as cheap as possible, they may generate their internal clocks by using RC oscillators instead of crystal oscillators. One well-known LIN transceiver is Freescale's MC33399. The LIN consortium specified the LIN with regard to the physical and the data link layer (i.e., layers 1 and 2 of the OSI model). As LIN has been primarily designed for automobiles the LIN standard defines the supply voltages for a LIN node to be between 7 volts and 18 volts (typically 12 volts), which makes LIN standard-compliant nodes unsuitable for applications in trucks (lorries) and busses as these typically use power supplies which provide supply voltages of 24 volts. The present disclosure addresses solutions to problems arising when connecting standard LIN nodes to a non-standard 24 volt power supply.